Inflammatory bone marrow microenvironment

Differential inflammatory conditioning of the bone marrow by acute myeloid leukemia and its impact on progression

ABSTRACT

Inflammation promotes solid tumor progression, but how regulatory mechanisms of inflammation may affect leukemia is less well studied. Using annexin A5 (ANXA5), a calcium-binding protein known for apoptosis, which we discovered to be differentially expressed in the bone marrow microenvironment (BMM) of mice with acute myeloid (AML) vs chronic myeloid leukemia, as a model system, we unravel here a circuit in which AML-derived tumor necrosis factor α (TNF-α) dose-dependently reduces ANXA5 in the BMM. This creates an inflammatory BMM via elevated levels of prostaglandin E2 (PGE2). Via binding to its EP4 receptor, PGE2 increases β-catenin and hypoxia-inducible factor 1α signaling in AML cells, thereby accelerating PGE2-sensitive AML. Human trephine biopsies may show lower ANXA5 expression and higher PGE2 expression in AML than other hematologic malignancies. Furthermore, syngeneic and xenogeneic transplantation models suggest a survival benefit after treatment with the inhibitor of prostaglandin-endoperoxide synthase 2 (cyclooxygenase 2 [COX2]), celecoxib, plus cytarabine in those AML types highly sensitive to PGE2 compared with cytarabine alone. Taken together, TNF-α/ANXA5/NF-κB/COX2/PGE2-mediated inflammation influences AML course in a highly differential and circular manner, and patients with AML with "inflammatory AML" may benefit from antiphlogistic agents as adjunct therapy.

CXCR4-enriched T regulatory cells preferentially home to bone marrow and resolve inflammation

CXCR4 cell surface expression is critical for the homing of T regulatory (Treg) cells to the bone marrow (BM). We hypothesize that CXCR4 enrichment on Tregs cell surface may abbreviate their transit time to reach BM. Umbilical cord-blood CD25+ Tregs underwent CXCR4 dual enrichment and ex vivo expansion using the CRANE process to generate CXCR4-enriched Tregs (TregCXCR4) cells, which showed a faster migration across the Transwell membrane toward CXCL12/stromal cell-derived factor 1α (SDF1α) at 15, 30, and 60 min, when compared to unmanipulated Tregcontrol cells (p < 0.0001). TregCXCR4 exhibited preferential homing to BM in vivo at 12 and 24 h. Metacluster analysis of BM showed a decrease in CD8+ and an increase in CD39 and CD73 and CXCR5 when compared to Tregcontrol. TregCXCR4 decreased plasma TGF-β1/β2 and IFN-γ levels. When compared to control, TregCXCR4 cells decreased in CD8+ T cell, IFN-γ, and TNF-α expression in BM. We conclude that TregCXCR4 show enhanced migration toward CXCL12/SDF1α and a preferential homing to BM resulting in resolution of inflammation.

Increased CXCL10 (IP-10) is associated with advanced myeloproliferative neoplasms and its loss dampens erythrocytosis in mouse models

Key studies in pre-leukemic disorders have linked increases in pro-inflammatory cytokines with accelerated phases of the disease, but the precise role of the cellular microenvironment in disease initiation and evolution remains poorly understood. In myeloproliferative neoplasms (MPNs), higher levels of specific cytokines have been previously correlated with increased disease severity (tumor necrosis factor-alpha [TNF-α], interferon gamma-induced protein-10 [IP-10 or CXCL10]) and decreased survival (interleukin 8 [IL-8]). Whereas TNF-α and IL-8 have been studied by numerous groups, there is a relative paucity of studies on IP-10 (CXCL10). Here we explore the relationship of IP-10 levels with detailed genomic and clinical data and undertake a complementary cytokine screen alongside functional assays in a wide range of MPN mouse models. Similar to patients, levels of IP-10 were increased in mice with more severe disease phenotypes (e.g., JAK2V617F/V617F TET2-/- double-mutant mice) compared with those with less severe phenotypes (e.g., CALRdel52 or JAK2+/V617F mice) and wild-type (WT) littermate controls. Although exposure to IP-10 did not directly alter proliferation or survival in single hematopoietic stem cells (HSCs) in vitro, IP-10-/- mice transplanted with disease-initiating HSCs developed an MPN phenotype more slowly, suggesting that the effect of IP-10 loss was noncell-autonomous. To explore the broader effects of IP-10 loss, we crossed IP-10-/- mice into a series of MPN mouse models and showed that its loss reduces the erythrocytosis observed in mice with the most severe phenotype. Together, these data point to a potential role for blocking IP-10 activity in the management of MPNs.

Immune effector cell-associated haematotoxicity after CAR T-cell therapy: from mechanism to management

Genetically engineered chimeric antigen receptor (CAR) T cells have become an effective treatment option for several advanced B-cell malignancies. Haematological side-effects, classified in 2023 as immune effector cell-associated haematotoxicity (ICAHT), are very common and can predispose for clinically relevant infections. As haematopoietic reconstitution after CAR T-cell therapy differs from chemotherapy-associated myelosuppression, a novel classification system for early and late ICAHT has been introduced. Furthermore, a risk stratification score named CAR-HEMATOTOX has been developed to identify candidates at high risk of ICAHT, thereby enabling risk-based interventional strategies. Therapeutically, growth factor support with granulocyte colony-stimulating factor (G-CSF) is the mainstay of treatment, with haematopoietic stem cell (HSC) boosts available for patients who are refractory to G-CSF (if available). Although the underlying pathophysiology remains poorly understood, translational studies from the past 3 years suggest that CAR T-cell-induced inflammation and baseline haematopoietic function are key contributors to prolonged cytopenia. In this Review, we provide an overview of the spectrum of haematological toxicities after CAR T-cell therapy and offer perspectives on future translational and clinical developments.

Hyperlipidemia-induced hematopoiesis is repressed by MLKL in endothelial cells of the splenic niche

Dysregulation of the hematopoietic niche during hyperlipidemia facilitates pathologic leukocyte production, driving atherogenesis. Although definitive hematopoiesis occurs primarily in the bone marrow, during atherosclerosis this also occurs in the spleen. Cells of the bone marrow niche, particularly endothelial cells, have been studied in atherosclerosis, although little is known about how splenic endothelial cells respond to the atherogenic environment. Here we show unique dysregulated pathways in splenic compared to bone marrow endothelial cells during atherosclerosis, including perturbations of lipid metabolism and endocytic trafficking pathways. As part of this response, we identify the mixed lineage kinase domain-like (MLKL) protein as a repressor of splenic, but not bone marrow, myelopoiesis. Silencing MLKL in splenic endothelial cells results in inefficient endosomal trafficking and lipid accumulation, ultimately promoting the production of myeloid cells that participate in plaque development. These studies identify endocytic trafficking by MLKL as a key mechanism of splenic endothelial cell maintenance, splenic hematopoiesis and, subsequently, atherosclerosis.

Gut Microbiota Composition Correlates with Disease Severity in Myelodysplastic Syndrome

The myelodysplastic syndrome (MDS) is a heterogeneous group of clonal disorders of hematopoietic progenitor cells related to ineffective hematopoiesis and an increased risk of transformation to acute myelogenous leukemia. MDS is divided into categories, namely lineage dysplasia (MDS-SLD), MDS with ring sideroblasts (MDS-RS), MDS with multilineage dysplasia (MDS-MLD), MDS with excess blasts (MDS-EB). The International Prognostic Classification System (IPSS) ranks the patients as very low, low, intermediate, high, and very high based on disease evolution and survival rates. Evidence points to toll-like receptor (TLR) abnormal signaling as an underlying mechanism of this disease, providing a link between MDS and immune dysfunction. Microbial signals, such as lipopolysaccharides from gram-negative bacteria, can activate or suppress TLRs. Therefore, we hypothesized that MDS patients present gut microbiota alterations associated with disease subtypes and prognosis. To test this hypothesis, we sequenced the 16S rRNA gene from fecal samples of 30 MDS patients and 16 healthy elderly controls. We observed a negative correlation between Prevotella spp. and Akkermansia spp. in MDS patients compared with the control group. High-risk patients presented a significant increase in the genus Prevotella spp. compared to the other risk categories. There was a significant reduction in the abundance of the genus Akkermansia spp. in high-risk patients compared with low- and intermediate-risk. There was a significant decrease in the genus Ruminococcus spp. in MDS-EB patients compared with controls. Our findings show a new association between gut dysbiosis and higher-risk MDS, with a predominance of gram-negative bacteria.

Bone marrow macrophages are involved in the ineffective hematopoiesis of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of heterogeneous myeloid clonal disorders characterized by ineffective hematopoiesis. Accumulating evidence has shown that macrophages (MΦs) are important components in the regulation of tumor progression and hematopoietic stem cells (HSCs). However, the roles of bone marrow (BM) MΦs in regulating normal and malignant hematopoiesis in different clinical stages of MDS are largely unknown. Age-paired patients with lower-risk MDS (N = 15), higher-risk MDS (N = 15), de novo acute myeloid leukemia (AML) (N = 15), and healthy donors (HDs) (N = 15) were enrolled. Flow cytometry analysis showed increased pro-inflammatory monocyte subsets and a decreased classically activated (M1) MΦs/alternatively activated (M2) MΦs ratio in the BM of patients with higher-risk MDS compared to lower-risk MDS. BM MФs from patients with higher-risk MDS and AML showed impaired phagocytosis activity but increased migration compared with lower-risk MDS group. AML BM MΦs showed markedly higher S100A8/A9 levels than lower-risk MDS BM MΦs. More importantly, coculture experiments suggested that the HSC supporting abilities of BM MΦs from patients with higher-risk MDS decreased, whereas the malignant cell supporting abilities increased compared with lower-risk MDS. Gene Ontology enrichment comparing BM MΦs from lower-risk MDS and higher-risk MDS for genes was involved in hematopoiesis- and immunity-related pathways. Our results suggest that BM MΦs are involved in ineffective hematopoiesis in patients with MDS, which indicates that repairing aberrant BM MΦs may represent a promising therapeutic approach for patients with MDS.

Micro-environment alterations through time leading to myeloid malignancies

The micro-environment plays a critical role in haematopoietic stem cell (HSC) development, self-renewal, differentiation and maintenance by providing a supportive cellular framework and essential molecular cues to sustain homeostasis. In ageing and development of age-related clonal haematopoiesis, the combined contribution of intrinsic alterations in haematopoietic stem cells and their surrounding micro-environment can promote myeloid skewing and release of pro-inflammatory cytokines. A pro-inflammatory micro-environment is a common feature in the initiation and sustenance of several myeloid malignancies. Furthermore, remodelling of the micro-environment is recognized to potentiate the survival of malignant over normal cells. This review explores micro-environmental interactions in the haematopoietic system of adults, especially how the bone marrow micro-environment is impacted by ageing, the onset of age-related clonal haematopoiesis and the development of myeloid malignancies. In addition, we also discuss the possible role age-related clonal haematopoiesis and chronic inflammatory conditions play in altering the bone marrow micro-environment dynamics. Finally, we explore the importance of in vitro models that accurately mimic different aspects of the bone marrow micro-environment in order to study normal and malignant haematopoiesis. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Multiparametric analysis of etoposide exposed mesenchymal stem cells and Fanconi anemia cells: implications in development of secondary myeloid malignancy

Secondary acute myeloid leukemia (sAML) may develop following a prior therapy or may evolve from an antecedent hematological disorder such as Fanconi Anemia (FA). Pathophysiology of leukemic evolution is not clear. Etoposide (Eto) is a chemotherapeutic agent implicated in development of sAML. FA is an inherited bone marrow (BM) failure disease characterized by genomic instability and xenobiotic susceptibility. Here, we hypothesized that alterations in the BM niche may play a critical/driver role in development of sAML in both conditions. Expression of selected genes involved in xenobiotic metabolism, DNA double-strand break response, endoplasmic reticulum (ER) stress, heat shock response and cell cycle regulation were determined in BM mesenchymal stem cells (MSCs) of healthy controls and FA patients at steady state and upon exposure to Eto at different concentrations and in recurrent doses. Expression of CYPA1, p53, CCNB1, Dicer1, CXCL12, FLT3L and TGF-Beta genes were significantly downregulated in FA-MSCs compared with healthy controls. Eto exposure induced significant alterations in healthy BM-MSCs with increased expression of CYP1A1, GAD34, ATF4, NUPR1, CXCL12, KLF4, CCNB1 and nuclear localization of Dicer1. Interestingly, FA-MSCs did not show significant alterations in these genes upon Eto exposure. As opposed to healthy MSCs DICER1 gene expression and intracellular localization was not altered on FA BM-MSCs after Eto treatment. These results showed that Eto is a highly potent molecule and has pleiotropic effects on BM-MSCs, FA cells show altered expression profile compared to healthy controls and Eto exposure on FA cells shows differential profile than healthy controls.

Clodronate liposomes may biases MSC differentiation toward adipogenesis through activation of NLRP3

Introduction

Clodronate-Liposomes (Clod-Lipo) injection after hematopoietic stem cell transplantation (HSCT) has been shown to be detrimental to hematopoietic reconstitution after transplantation, and our previous study showed that Clod-Lipo injection after HSCT increased adipocytes in the bone marrow cavity of mice after HSCT, but the reason for the large increase in adipocytes has not been clearly explained. The aim of this study was to investigate the source and mechanism of bone marrow cavity adipocytes after HSCT injection of Clod-Lipo.

Methods

BALB/c mice received 7.5 Gy of total body irradiation followed by infusion of 5x106 bone marrow mononuclear cells from C57BL/6 via the tail vein. Clod-Lipo were injected through the tail vein on the first day after HSCT and every 5 days for the rest of the day. BALB/c mice were then divided into three groups: BMT, BMT + Clodronate-Liposomes (BMT + Clod-Lipo), and BMT + PBS-Liposomes (BMT + PBS-Lipo). Bone marrow pathological changes were detected by H&E staining, Western blot was used to detect the expression of NLRP3 and Caspase-1 in mouse bone marrow cells, and RT-qPCR was used to detect the expression levels of the key transcription factors peroxisome proliferator-activated receptor γ (PPAR-γ) and CCAAT/enhancer binding protein (C/EBPα) mRNA in bone marrow cells. Mouse mesenchymal stem cells (MSC) cultured in vitro were identified by flow cytometry, and adipocyte induction assays were performed using Clod-Lipo action for 24 h, Oil red staining was used to identify adipogenesis. Western blot was performed to detect NLRP3 and caspase-1 expression in MSC after Clod-Lipo action. Caspase-1 was blocked with Ac-YVAD-cmk (Ac-YV), followed by adipogenesis assay after 24 h of Clod-Lipo action to observe the change in the amount of adipogenesis.

Results

Compared with the other two groups, a significant increase in adipocytes was found in the Clod-Lipo group by HE staining, and increased expression of NLRP3 and Caspase-1 in mouse bone marrow cells was found by western Blot. By culturing MSC in vitro and performing adipogenesis assay after 24 h of Clod-Lipo action, it was found that adipogenesis was increased in the Clod-Lipo group, while the expression of NLRP3 and Caspase-1 was increased in MSCs, and adipogenesis assay was performed after 2 h of action using Caspase-1 inhibitor, and it was found that adipocytes was reduced.

Conclusions

The results of this study suggest that MSC are biased towards adipocyte generation in response to Clod-Lipo, a process that may be associated with activation of the NLRP3/caspase-1 pathway.

Offspring affected with in utero Zika virus infection retain molecular footprints in the bone marrow and blood cells

Congenital virus infections, for example cytomegalovirus and rubella virus infections, commonly affect the central nervous and hematological systems in fetuses and offspring. However, interactions between emerging congenital Zika virus and hematological system-bone marrow and blood-in fetuses and offspring are mainly unknown. Our overall goal was to determine whether silent in utero Zika virus infection can cause functional and molecular footprints in the bone marrow and blood of fetuses and offspring. We specifically focused on silent fetal infection because delayed health complications in initially asymptomatic offspring were previously demonstrated in animal and human studies. Using a well-established porcine model for Zika virus infection and a set of cellular and molecular experimental tools, we showed that silent in utero infection causes multi-organ inflammation in fetuses and local inflammation in the fetal bone marrow. In utero infection also caused footprints in the offspring bone marrow and PBMCs. These findings should be considered in a broader clinical context because of growing concerns about health sequelae in cohorts of children affected with congenital Zika virus infection in the Americas. Understanding virus-induced molecular mechanisms of immune activation and inflammation in fetuses may provide targets for early in utero interventions. Also, identifying early biomarkers of in utero-acquired immunopathology in offspring may help to alleviate long-term sequelae.

Myeloperoxidase creates a permissive microenvironmental niche for the progression of multiple myeloma

Expression of myeloperoxidase (MPO), a key inflammatory enzyme restricted to myeloid cells, is negatively associated with the development of solid tumours. Activated myeloid cell populations are increased in multiple myeloma (MM); however, the functional consequences of myeloid-derived MPO within the myeloma microenvironment are unknown. Here, the role of MPO in MM pathogenesis was investigated, and the capacity for pharmacological inhibition of MPO to impede MM progression was evaluated. In the 5TGM1-KaLwRij mouse model of myeloma, the early stages of tumour development were associated with an increase in CD11b+ myeloid cell populations and an increase in Mpo expression within the bone marrow (BM). Interestingly, MM tumour cell homing was increased towards sites of elevated myeloid cell numbers and MPO activity within the BM. Mechanistically, MPO induced the expression of key MM growth factors, resulting in tumour cell proliferation and suppressed cytotoxic T-cell activity. Notably, tumour growth studies in mice treated with a small-molecule irreversible inhibitor of MPO (4-ABAH) demonstrated a significant reduction in overall MM tumour burden. Taken together, our data demonstrate that MPO contributes to MM tumour growth, and that MPO-specific inhibitors may provide a new therapeutic strategy to limit MM disease progression.

MacroH2A1.1 as a crossroad between epigenetics, inflammation and metabolism of mesenchymal stromal cells in myelodysplastic syndromes

Ineffective hematopoiesis is a hallmark of myelodysplastic syndromes (MDS). Hematopoietic alterations in MDS patients strictly correlate with microenvironment dysfunctions, eventually affecting also the mesenchymal stromal cell (MSC) compartment. Stromal cells are indeed epigenetically reprogrammed to cooperate with leukemic cells and propagate the disease as "tumor unit"; therefore, changes in MSC epigenetic profile might contribute to the hematopoietic perturbations typical of MDS. Here, we unveil that the histone variant macroH2A1 (mH2A1) regulates the crosstalk between epigenetics and inflammation in MDS-MSCs, potentially affecting their hematopoietic support ability. We show that the mH2A1 splicing isoform mH2A1.1 accumulates in MDS-MSCs, correlating with the expression of the Toll-like receptor 4 (TLR4), an important pro-tumor activator of MSC phenotype associated to a pro-inflammatory behavior. MH2A1.1-TLR4 axis was further investigated in HS-5 stromal cells after ectopic mH2A1.1 overexpression (mH2A1.1-OE). Proteomic data confirmed the activation of a pro-inflammatory signature associated to TLR4 and nuclear factor kappa B (NFkB) activation. Moreover, mH2A1.1-OE proteomic profile identified several upregulated proteins associated to DNA and histones hypermethylation, including S-adenosylhomocysteine hydrolase, a strong inhibitor of DNA methyltransferase and of the methyl donor S-adenosyl-methionine (SAM). HPLC analysis confirmed higher SAM/SAH ratio along with a metabolic reprogramming. Interestingly, an increased LDHA nuclear localization was detected both in mH2A1.1-OE cells and MDS-MSCs, probably depending on MSC inflammatory phenotype. Finally, coculturing healthy mH2A1.1-OE MSCs with CD34+ cells, we found a significant reduction in the number of CD34+ cells, which was reflected in a decreased number of colony forming units (CFU-Cs). These results suggest a key role of mH2A1.1 in driving the crosstalk between epigenetic signaling, inflammation, and cell metabolism networks in MDS-MSCs.

Abnormal adipogenic signaling in the bone marrow mesenchymal stem cells contributes to supportive microenvironment for leukemia development

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive hematological malignancy, associated with unfavorable patient outcome, primarily due to disease relapse. Mesenchymal stem cells (MSCs) residing in the bone marrow (BM) niche are the source of mesenchyma-derived subpopulations, including adipocytes, and osteocytes, that are critical for normal hematopoiesis. This study aimed to characterize BM-derived adipocyte/osteocyte fractions and their crosstalk with AML cells as a potential mechanism underlying leukemogenesis.

METHODS

BM cell subpopulations derived from primary AML patients were evaluated using humanized ex-vivo and in-vivo models, established for this study. The models comprised AML blasts, normal hematopoietic stem and progenitor cells and mesenchymal stromal subpopulations. ELISA, FACS analysis, colony forming unit assay, whole exome sequencing and real-time qPCR were employed to assess the differentiation capacity, genetic status, gene expression and function of these cell fractions. To explore communication pathways between AML cells and BM subpopulations, levels of signaling mediators, including cytokines and chemokines, were measured using the ProcartaPlex multiplex immunoassay.

RESULTS

The study revealed deficiencies in adipogenic/osteogenic differentiation of BM-MSCs derived from AML patients, with adipocytes directly promoting survival and clonogenicity of AML cells in-vitro. In whole exome sequencing of BM-MSC/stromal cells, the AHNAK2 gene, associated with the stimulation of adipocyte differentiation, was found to be mutated and significantly under-expressed, implying its abnormal function in AML. The evaluation of communication pathways between AML cells and BM subpopulations demonstrated pronounced alterations in the crosstalk between these cell fractions. This was reflected by significantly elevated levels of signaling mediators cytokines/chemokines, in AML-induced adipocytes/osteocytes compared to non-induced MSCs, indicating abnormal hematopoiesis. Furthermore, in-vivo experiments using a fully humanized 3D scaffold model, showed that AML-induced adipocytes were the dominant component of the tumor microenvironment, providing preferential support to leukemia cell survival and proliferation.

CONCLUSIONS

This study has disclosed direct contribution of impaired functional, genetic and molecular properties of AML patient-derived adipocytes to effective protection of AML blasts from apoptosis and to stimulation of their growth in vitro and in vivo, which overall leads to disease propagation and relapse. The detected AHNAK2 gene mutations in AML-MSCs point to their involvement in the mechanism underlying abnormal adipogenesis. Video Abstract.

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

Concomitant induction of SLIT3 and microRNA-218-2 in macrophages by toll-like receptor 4 activation limits osteoclast commitment

BACKGROUND

Toll-like receptor 4 (TLR4) conducts a highly regulated inflammatory process by limiting the extent of inflammation to avoid toxicity and tissue damage, even in bone tissues. Thus, it is plausible that strategies for the maintenance of normal bone-immunity to prevent undesirable bone damage by TLR4 activation can exist, but direct evidence is still lacking.

METHODS

Osteoclast precursors (OCPs) obtained from WT or Slit3-deficient mice were differentiated into osteoclast (OC) with macrophage colony-stimulating factor (M-CSF), RANK ligand (RANKL) and lipopolysaccharide (LPS) by determining the number of TRAP-positive multinuclear cells (TRAP+ MNCs). To determine the alteration of OCPs population, fluorescence-activated cell sorting (FACS) was conducted in bone marrow cells in mice after LPS injection. The severity of bone loss in LPS injected WT or Slit3-deficient mice was evaluated by micro-CT analysis.

RESULT

We demonstrate that TLR4 activation by LPS inhibits OC commitment by inducing the concomitant expression of miR-218-2-3p and its host gene, Slit3, in mouse OCPs. TLR4 activation by LPS induced SLIT3 and its receptor ROBO1 in BMMs, and this SLIT3-ROBO1 axis hinders RANKL-induced OC differentiation by switching the protein levels of C/EBP-β isoforms. A deficiency of SLIT3 resulted in increased RANKL-induced OC differentiation, and the elevated expression of OC marker genes including Pu.1, Nfatc1, and Ctsk. Notably, Slit3-deficient mice showed expanded OCP populations in the bone marrow. We also found that miR-218-2 was concomitantly induced with SLIT3 expression after LPS treatment, and that this miRNA directly suppressed Tnfrsf11a (RANK) expression at both gene and protein levels, linking it to a decrease in OC differentiation. An endogenous miR-218-2 block rescued the expression of RANK and subsequent OC formation in LPS-stimulated OCPs. Aligned with these results, SLIT3-deficient mice displayed increased OC formation and reduced bone density after LPS challenge.

CONCLUSION

Our findings suggest that the TLR4-dependent concomitant induction of Slit3 and miR-218-2 targets RANK in OCPs to restrain OC commitment, thereby avoiding an uncoordinated loss of bone through inflammatory processes. These observations provide a mechanistic explanation for the role of TLR4 in controlling the commitment phase of OC differentiation. Video Abstract.

Increased Bone Marrow Uptake and Accumulation of Very-Late Antigen-4 Targeted Lipid Nanoparticles

Lipid nanoparticles (LNPs) have evolved rapidly as promising delivery systems for oligonucleotides, including siRNAs. However, current clinical LNP formulations show high liver accumulation after systemic administration, which is unfavorable for the treatment of extrahepatic diseases, such as hematological disorders. Here we describe the specific targeting of LNPs to hematopoietic progenitor cells in the bone marrow. Functionalization of the LNPs with a modified Leu-Asp-Val tripeptide, a specific ligand for the very-late antigen 4 resulted in an improved uptake and functional siRNA delivery in patient-derived leukemia cells when compared to their non-targeted counterparts. Moreover, surface-modified LNPs displayed significantly improved bone-marrow accumulation and retention. These were associated with increased LNP uptake by immature hematopoietic progenitor cells, also suggesting similarly improved uptake by leukemic stem cells. In summary, we describe an LNP formulation that successfully targets the bone marrow including leukemic stem cells. Our results thereby support the further development of LNPs for targeted therapeutic interventions for leukemia and other hematological disorders.

Systems pharmacology reveals the mechanism of Astragaloside IV in improving immune activity on cyclophosphamide-induced immunosuppressed mice

ETHNOPHARMACOLOGICAL RELEVANCE

Myelosuppression, also known as bone marrow suppression (BMS), is a pathological phenomenon of the decrease in the production of blood cells and further lead to immune homeostasis disorder. Astragalus mongholicus Bunge (AM, checked with The World Flora Online, http://www.worldfloraonline.org, updated on January 30, 2023) is a traditional Chinese medicine with efficacy of tonifying Qi and strengthening body immunity in thousands of years of clinical practice in China. Astragaloside IV (AS-IV) is a major active ingredient of AM, which plays an important role in regulating immune system through different ways.

AIM OF THE STUDY

This study was aimed to investigate the protective effect and mechanism of AS-IV on macrophages in vitro and cyclophosphamide (CTX)-induced immunosuppressive mice in vivo, and to provide experimental basis for the prevention and treatment of AS-IV in myelosuppression.

MATERIALS AND METHODS

Based on network pharmacology and molecular docking technology, the core targets and signaling pathways of saponins of AM against myelosuppression were screened. And then, the immunoregulatory effect of AS-IV on RAW264.7 cells was investigated by cellular immune activity and cellular secretion analysis in vitro. In this way, the effects of AS-IV on the main potential targets of HIF-1α/NF-κB signaling pathway were analyzed by qRT-PCR and Western blot methods. Furthermore, comprehensive analysis of the effects of AS-IV against CTX-induced mice were conducted on the basis of immune organs indices analysis, histopathological analysis, hematological analysis, natural killer cell activity analysis and spleen lymphocyte transformation activity analysis. In order to further verify the relationship between active ingredients and action targets, drug inhibitor experiments were finally conducted.

RESULTS

AS-IV, as a potential anti-myelosuppressive compound, was screened by systematic pharmacological methods to act on target genes including HIF1A and RELA together with the HIF-1α/NF-κB signaling pathway. Further studies by molecular docking technology showed that AS-IV had good binding activity with HIF1A, RELA, TNF, IL6, IL1B and other core targets. Besides, cellular and animal experiments validation results showed that AS-IV could enhance the migration and phagocytosis of RAW264.7 cells, and protect the immune organs such as spleen and thymus together with bone tissues from damage. By this means, immune cell function including spleen natural killer cell and lymphocyte transformation activity were also enhanced. In addition, white blood cells, red blood cells, hemoglobin, platelets and bone marrow cells were also significantly improved in the suppressed bone marrow microenvironment (BMM). In kinetic experiments, the secretion of cytokines such as TNF-α, IL-6 and IL-1β were increased, and IL-10, TGF-β1 were decreased. The key regulatory proteins such as HIF-1α, NF-κB, PHD3 in HIF-1α/NF-κB signaling pathway were also regulated in the results of upregulated expression of HIF-1α, p-NF-κB p65 and PHD3 at the protein or mRNA level. Finally, the inhibition experiment results suggested that AS-IV could significantly improve protein response in immunity and inflammation such as HIF-1α, NF-κB and PHD3.

CONCLUSION

AS-IV could significantly relieve CTX-induced immunosuppressive and might improve the immune activity of macrophages by activating HIF-1α/NF-κB signaling pathway, and provide a reliable basis for the clinical application of AS-IV as a potentially valuable regulator of BMM.

Uncovering perturbations in human hematopoiesis associated with healthy aging and myeloid malignancies at single-cell resolution

Early hematopoiesis is a continuous process in which hematopoietic stem and progenitor cells (HSPCs) gradually differentiate toward specific lineages. Aging and myeloid malignant transformation are characterized by changes in the composition and regulation of HSPCs. In this study, we used single-cell RNA sequencing (scRNA-seq) to characterize an enriched population of human HSPCs obtained from young and elderly healthy individuals.

Based on their transcriptional profile, we identified changes in the proportions of progenitor compartments during aging, and differences in their functionality, as evidenced by gene set enrichment analysis. Trajectory inference revealed that altered gene expression dynamics accompanied cell differentiation, which could explain aging-associated changes in hematopoiesis. Next, we focused on key regulators of transcription by constructing gene regulatory networks (GRNs) and detected regulons that were specifically active in elderly individuals. Using previous findings in healthy cells as a reference, we analyzed scRNA-seq data obtained from patients with myelodysplastic syndrome (MDS) and detected specific alterations of the expression dynamics of genes involved in erythroid differentiation in all patients with MDS such as TRIB2. In addition, the comparison between transcriptional programs and GRNs regulating normal HSPCs and MDS HSPCs allowed identification of regulons that were specifically active in MDS cases such as SMAD1, HOXA6, POU2F2, and RUNX1 suggesting a role of these transcription factors (TFs) in the pathogenesis of the disease.

In summary, we demonstrate that the combination of single-cell technologies with computational analysis tools enable the study of a variety of cellular mechanisms involved in complex biological systems such as early hematopoiesis and can be used to dissect perturbed differentiation trajectories associated with perturbations such as aging and malignant transformation. Furthermore, the identification of abnormal regulatory mechanisms associated with myeloid malignancies could be exploited for personalized therapeutic approaches in individual patients.

Clonal hematopoiesis, somatic mosaicism, and age-associated disease

Somatic mosaicism, the occurrence of multiple genetically distinct cell clones within the same tissue, is an evitable consequence of human aging. The hematopoietic system is no exception to this, where studies have revealed the presence of expanded blood cell clones carrying mutations in preleukemic driver genes and/or genetic alterations in chromosomes. This phenomenon is referred to as clonal hematopoiesis and is remarkably prevalent in elderly individuals. While clonal hematopoiesis represents an early step toward a hematological malignancy, most individuals will never develop blood cancer. Somewhat unexpectedly, epidemiological studies have found that clonal hematopoiesis is associated with an increase in the risk of all-cause mortality and age-related disease, particularly in the cardiovascular system. Studies using murine models of clonal hematopoiesis have begun to shed light on this relationship, suggesting that driver mutations in mature blood cells can causally contribute to aging and disease by augmenting inflammatory processes. Here we provide an up-to-date review of clonal hematopoiesis within the context of somatic mosaicism and aging and describe recent epidemiological studies that have reported associations with age-related disease. We will also discuss the experimental studies that have provided important mechanistic insight into how driver mutations promote age-related disease and how this knowledge could be leveraged to treat individuals with clonal hematopoiesis.

Circulating mitochondrial DNA is associated with anemia in newly diagnosed hematologic malignancies

Recent reports discovered that red blood cells (RBCs) could scavenge cell-free mitochondrial DNA (mtDNA), which drives the accelerated erythrophagocytosis and innate immune activation characterized by anemia and inflammatory cytokine production. However, the clinical value of the circulating mtDNA copy number alterations in hematologic malignancies is poorly understood. Our data showed that in comparison to healthy group, the patients group had significantly higher mtDNA and histone H4 levels. Moreover, we observed that RBC-bound mtDNA and histone H4 were negatively correlated with hemoglobin in patients. In addition, cytokines and chemokines levels in patients differed significantly from normal controls (21 higher, 7 lower). Our study suggested that both circulating mtDNA and histone H4 were associated with anemia in hematologic malignancies, which helps to further understand the potential mechanism of anemia development in patients with hematologic malignancies. This information may play a vital role in the specific therapeutic interventions for leukemia in the future.

Pseudolycorine chloride ameliorates Th17 cell-mediated central nervous system autoimmunity by restraining myeloid-derived suppressor cell expansion

CONTEXT

The alkaloids of Narcissus tazetta L. var. Chinensis Roem (Amaryllidaceae) have antitumor and antiviral activities. However, the immunopharmacological effects of one of its constituents, pseudolycorine chloride (PLY), have not been reported yet.

OBJECTIVE

We evaluated the effect of PLY on myeloid-derived suppressor cells (MDSCs) expansion and differentiation into monocyte-like MDSCs (M-MDSCs) and examined whether PLY alleviates Th17 cell-mediated experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS).

MATERIALS AND METHODS

In vitro, MDSCs were treated with PLY (0.67, 2 and 6 μM) or solcitinib (10 μM, positive control) for 48 or 96 h, and their proliferation, expansion, and differentiation into M-MDSCs were examined by flow cytometry. Myelin oligodendrocyte glycoprotein (MOG_35-55) was used to induce EAE in female C57BL/6 mice, and the mice were treated with 40 mg/kg/d PLY or 1 mg/kg/d FK-506 (tacrolimus, positive control) for 21 days. Inflammatory infiltration, spinal cord demyelination, and MDSCs and Th17 cells infiltration into the spinal cord were examined using haematoxylin and eosin staining, Luxol fast blue staining, and immunofluorescence, respectively.

RESULTS

In vitro, PLY (IC50/24 h = 6.18 μM) significantly inhibited IL-6 and GM-CSF-induced MDSCs proliferation, expansion and differentiation into M-MDSCs at all concentrations used. However, these concentrations did not show cytotoxicity. In mice, PLY (40 mg/kg) treatment alleviated EAE and inhibited inflammatory infiltration, demyelination, and MDSCs and Th17 cells infiltration into the spinal cord.

DISCUSSION AND CONCLUSIONS

PLY may be an excellent candidate for the treatment of MS and other autoimmune diseases.

Acquired and hereditary bone marrow failure: A mitochondrial perspective

The disorders known as bone marrow failure syndromes (BMFS) are life-threatening disorders characterized by absence of one or more hematopoietic lineages in the peripheral blood. Myelodysplastic syndromes (MDS) are now considered BMF disorders with associated cellular dysplasia. BMFs and MDS are caused by decreased fitness of hematopoietic stem cells (HSC) and poor hematopoiesis. BMF and MDS can occur de novo or secondary to hematopoietic stress, including following bone marrow transplantation or myeloablative therapy. De novo BMF and MDS are usually associated with specific genetic mutations. Genes that are commonly mutated in BMF/MDS are in DNA repair pathways, epigenetic regulators, heme synthesis. Despite known and common gene mutations, BMF and MDS are very heterogenous in nature and non-genetic factors contribute to disease phenotype. Inflammation is commonly found in BMF and MDS, and contribute to ineffective hematopoiesis. Another common feature of BMF and MDS, albeit less known, is abnormal mitochondrial functions. Mitochondria are the power house of the cells. Beyond energy producing machinery, mitochondrial communicate with the rest of the cells via triggering stress signaling pathways and by releasing numerous metabolite intermediates. As a result, mitochondria play significant roles in chromatin regulation and innate immune signaling pathways. The main goal of this review is to investigate BMF processes, with a focus mitochondria-mediated signaling in acquired and inherited BMF.

Higher red cell distribution width and poorer hospitalization-related outcomes in elderly patients

BACKGROUND

Red cell distribution width (RDW), an index for variation of red blood cell (RBC) size, has been proposed as a potential marker for poorer outcomes in several aging-related diseases and conditions. We tested whether greater variability of RBC size, presented as a higher RDW value, predicts poor prognoses among hospitalized patients over 60 years old.

METHODS

We retrospectively collected data from older hospitalized patients aged ≥60 years between January 2013 to December 2017 at Sutter Health, a large integrated health system in Northern California. The RDW was measured during hospital admission and categorized with 1% intervals (≤13.9, 14.0-14.9, 15.0-15.9, 16.0-16.9, 17.0-17.9 and ≥18.0%). The primary outcome was the rate of in-hospital mortality and secondary outcomes included 30-day re-admission rate and length of hospital stay (in days).

RESULTS

A total of 167,292 admissions from 94,617 patients were included. The overall in-hospital mortality rate was 6.3%. As the RDW value increased, the rate of in-hospital mortality gradually increased from 2.7% for the lowest RDW category to 12.2% in the highest category (p-trend <0.001). The overall 30-day re-admission rate after discharge was 12.5% and the rate of 30-day re-admission also increased with increasing RDW categories (7.4% in the lowest group vs. 15.8% in the highest group, p-trend <0.001). Patients with the highest RDW values at admission stayed 1.5-2.0 times longer in the hospital than patients with lower RDW values who were admitted for the same causes.

CONCLUSIONS

Greater variability of RBC size is significantly associated with worse prognosis in hospitalized elderly patients, indicating higher mortality, greater risk of early re-admission, and longer hospital stay days. Risk stratification strategies for hospitalized elderly should include RDW value.

Comparison of Laboratory Methods for the Clinical Follow Up of Checkpoint Blockade Therapies in Leukemia: Current Status and Challenges Ahead

The development of immune checkpoint inhibitors, the monoclonal antibodies that modulate the interaction between immune checkpoint molecules or their ligands on the immune cells or tumor tissue has revolutionized cancer treatment. While there are various studies proving their efficacy in hematological malignancies, there is also a body of accumulating evidence indicating that immune checkpoint inhibitors’ clinical benefits are limited in such diseases. In addition, due to their regulatory nature that balances the immune responses, blockade of immune checkpoints may lead to toxic side effects and autoimmune responses, and even primary or acquired resistance mechanisms may restrict their success. Thus, the need for laboratory biomarkers to identify and monitor patient populations who are more likely respond to this type of therapy and the management of side effects seem critical. However, guidelines regarding the use of immune checkpoint inhibitors in hematological cancers and during follow-up are limited while there is no consensus on the laboratory parameters to be investigated for safety and efficacy of the treatment. This review aims to provide an insight into recent information on predictive and prognostic value of biomarkers and laboratory tests for the clinical follow up of hematological malignancies, with an emphasis on leukemia.

Vascular Regulation of Hematopoietic Stem Cell Homeostasis, Regeneration, and Aging

Purpose of Review

Hematopoietic stem cells (HSCs) sit at the top of the hierarchy that meets the daily burden of blood production. HSC maintenance relies on extrinsic cues from the bone marrow (BM) microenvironment to balance stem cell self-renewal and cell fate decisions. In this brief review, we will highlight the studies and model systems that define the centralized role of BM vascular endothelium in modulating HSC activity in health and stress.

Recent Findings

The BM microenvironment is composed of a diverse array of intimately associated vascular and perivascular cell types. Recent dynamic imaging studies, coupled with single-cell RNA sequencing (scRNA-seq) and functional readouts, have advanced our understanding of the HSC-supportive cell types and their cooperative mechanisms that govern stem cell fate during homeostasis, regeneration, and aging. These findings have established complex and discrete vascular microenvironments within the BM that express overlapping and unique paracrine signals that modulate HSC fate.

Summary

Understanding the spatial and reciprocal HSC-niche interactions and the molecular mechanisms that govern HSC activity in the BM vascular microenvironment will be integral in developing therapies aimed at ameliorating hematological disease and supporting healthy hematopoietic output.

Targeting CD38 in acute myeloid leukemia interferes with leukemia trafficking and induces phagocytosis

Targeting the interaction between leukemic cells and the microenvironment is an appealing approach to enhance the therapeutic efficacy in acute myeloid leukemia (AML). AML infiltration induces a significant release of inflammatory cytokines in the human bone marrow niche which accelerates leukemogenesis. As the transmembrane glycoprotein CD38 has been shown to regulate cytokine release, we assessed the anti-leukemic potential of CD38 inhibition in AML. CD38 expression in AML cells proved to depend on microenvironmental cues and could be significantly enforced through addition of tretinoin. In fact, the anti-CD38 antibody daratumumab showed significant cytostatic efficacy in a 3D in vitro triple-culture model of AML, but with modest cell-autonomous cytotoxic activity and independent of CD38 expression level. In line with a predominantly microenvironment-mediated activity of daratumumab in AML, CD38 inhibition significantly induced antibody-dependent phagocytosis and showed interference with AML cell trafficking in vivo in a xenograft transplantation model, but overall lacked robust anti-leukemic effects.

Bone marrow derived stromal cells from myelodysplastic syndromes are altered but not clonally mutated in vivo

The bone marrow (BM) stroma in myeloid neoplasms is altered and it is hypothesized that this cell compartment may also harbor clonal somatically acquired mutations. By exome sequencing of in vitro expanded mesenchymal stromal cells (MSCs) from n = 98 patients with myelodysplastic syndrome (MDS) and n = 28 healthy controls we show that these cells accumulate recurrent mutations in genes such as ZFX (n = 8/98), RANK (n = 5/98), and others. MDS derived MSCs display higher mutational burdens, increased replicative stress, senescence, inflammatory gene expression, and distinct mutational signatures as compared to healthy MSCs. However, validation experiments in serial culture passages, chronological BM aspirations and backtracking of high confidence mutations by re-sequencing primary sorted MDS MSCs indicate that the discovered mutations are secondary to in vitro expansion but not present in primary BM. Thus, we here report that there is no evidence for clonal mutations in the BM stroma of MDS patients.

Bone marrow-derived mesenchymal stroma cells (MSCs) in myeloid neoplasia have been hypothesized to carry somatic mutations and contribute to pathogenesis. Here the authors analyse ex-vivo cultures and primary MSCs derived from patients with myelodysplastic syndromes, finding functional alterations but no evidence of clonal mutations.

Bone Marrow Microenvironment in Light-Chain Amyloidosis: In Vitro Expansion and Characterization of Mesenchymal Stromal Cells

Immunoglobulin light-chain amyloidosis (AL) is caused by misfolded light chains produced by a small B cell clone. Mesenchymal stromal cells (MSCs) have been reported to affect plasma cell behavior. We aimed to characterize bone marrow (BM)-MSCs from AL patients, considering functional aspects, such as proliferation, differentiation, and immunomodulatory capacities. MSCs were in vitro expanded from the BM of 57 AL patients and 14 healthy donors (HDs). MSC surface markers were analyzed by flow cytometry, osteogenic and adipogenic differentiation capacities were in vitro evaluated, and co-culture experiments were performed in order to investigate MSC immunomodulatory properties towards the ALMC-2 cell line and HD peripheral blood mononuclear cells (PBMCs). AL-MSCs were comparable to HD-MSCs for morphology, immune-phenotype, and differentiation capacities. AL-MSCs showed a reduced proliferation rate, entering senescence at earlier passages than HD-MSCs. The AL-MSC modulatory effect on the plasma-cell line or circulating plasma cells was comparable to that of HD-MSCs. To our knowledge, this is the first study providing a comprehensive characterization of AL-MSCs. It remains to be defined if the observed abnormalities are the consequence of or are involved in the disease pathogenesis. BM microenvironment components in AL may represent the targets for the prevention/treatment of the disease in personalized therapies.

Still a burning question: the interplay between inflammation and fibrosis in myeloproliferative neoplasms

PURPOSE OF REVIEW

Bone marrow fibrosis is the progressive replacement of blood-forming cells by reticulin fibres, caused by the acquisition of somatic mutations in hematopoietic stem cells. The molecular and cellular mechanisms that drive the progression of bone marrow fibrosis remain unknown, yet chronic inflammation appears to be a conserved feature in most patients suffering from myeloproliferative neoplasms.

RECENT FINDINGS

Here, we review recent literature pertaining to the role of inflammation in driving bone marrow fibrosis, and its effect on the various hematopoietic and nonhematopoietic cell populations.

SUMMARY

Recent evidence suggests that the pathogenesis of MPN is primarily driven by the hematopoietic stem and progenitor cells, together with their mutated progeny, which in turn results in chronic inflammation that disrupts the bone marrow niche and perpetuates a disease-permissive environment. Emerging data suggests that specifically targeting stromal inflammation in combination with JAK inhibition may be the way forward to better treat MPNs, and bone marrow fibrosis specifically.

Inflammation, Aging and Hematopoiesis: A Complex Relationship

All vertebrate blood cells descend from multipotent hematopoietic stem cells (HSCs), whose activity and differentiation depend on a complex and incompletely understood relationship with inflammatory signals. Although homeostatic levels of inflammatory signaling play an intricate role in HSC maintenance, activation, proliferation, and differentiation, acute or chronic exposure to inflammation can have deleterious effects on HSC function and self-renewal capacity, and bias their differentiation program. Increased levels of inflammatory signaling are observed during aging, affecting HSCs either directly or indirectly via the bone marrow niche and contributing to their loss of self-renewal capacity, diminished overall functionality, and myeloid differentiation skewing. These changes can have significant pathological consequences. Here, we provide an overview of the current literature on the complex interplay between HSCs and inflammatory signaling, and how this relationship contributes to age-related phenotypes. Understanding the mechanisms and outcomes of this interaction during different life stages will have significant implications in the modulation and restoration of the hematopoietic system in human disease, recovery from cancer and chemotherapeutic treatments, stem cell transplantation, and aging.

Clonal Hematopoiesis of Indeterminate Potential as a Novel Risk Factor for Donor-Derived Leukemia

Hematopoietic stem cell transplantation (HSCT) is a critical treatment modality for many hematological and non-hematological diseases that is being extended to treat older individuals. However, recent studies show that clonal hematopoiesis of indeterminate potential (CHIP), a common, asymptomatic condition characterized by the expansion of age-acquired somatic mutations in blood cell lineages, may be a risk factor for the development of donor-derived leukemia (DDL), unexplained cytopenias, and chronic graft-versus-host disease. CHIP may contribute to the pathogenesis of these significant transplant complications via various cell-autonomous and non-cell-autonomous mechanisms, and the clinical presentation of DDL may be broader than anticipated. A more comprehensive understanding of the contributions of CHIP to DDL may have important implications for the screening of donors and will improve the safety of HSCT. The objective of this review is to discuss studies linking DDL and CHIP and to explore potential mechanisms by which CHIP may contribute to DDL.

Inflammatory Pathophysiology as a Contributor to Myeloproliferative Neoplasms

Myeloid neoplasms, including acute myeloid leukemia (AML), myeloproliferative neoplasms (MPNs), and myelodysplastic syndromes (MDS), feature clonal dominance and remodeling of the bone marrow niche in a manner that promotes malignant over non-malignant hematopoiesis. This take-over of hematopoiesis by the malignant clone is hypothesized to include hyperactivation of inflammatory signaling and overproduction of inflammatory cytokines. In the Ph-negative MPNs, inflammatory cytokines are considered to be responsible for a highly deleterious pathophysiologic process: the phenotypic transformation of polycythemia vera (PV) or essential thrombocythemia (ET) to secondary myelofibrosis (MF), and the equivalent emergence of primary myelofibrosis (PMF). Bone marrow fibrosis itself is thought to be mediated heavily by the cytokine TGF-β, and possibly other cytokines produced as a result of hyperactivated JAK2 kinase in the malignant clone. MF also features extramedullary hematopoiesis and progression to bone marrow failure, both of which may be mediated in part by responses to cytokines. In MF, elevated levels of individual cytokines in plasma are adverse prognostic indicators: elevated IL-8/CXCL8, in particular, predicts risk of transformation of MF to secondary AML (sAML). Tumor necrosis factor (TNF, also known as TNFα), may underlie malignant clonal dominance, based on results from mouse models. Human PV and ET, as well as MF, harbor overproduction of multiple cytokines, above what is observed in normal aging, which can lead to cellular signaling abnormalities separate from those directly mediated by hyperactivated JAK2 or MPL kinases. Evidence that NFκB pathway signaling is frequently hyperactivated in a pan-hematopoietic pattern in MPNs, including in cells outside the malignant clone, emphasizes that MPNs are pan-hematopoietic diseases, which remodel the bone marrow milieu to favor persistence of the malignancy. Clinical evidence that JAK2 inhibition by ruxolitinib in MF neither reliably reduces malignant clonal burden nor eliminates cytokine elevations, suggests targeting cytokine mediated signaling as a therapeutic strategy, which is being pursued in new clinical trials. Greater knowledge of inflammatory pathophysiology in MPNs can therefore contribute to the development of more effective therapy.

Secondary CNL after SAA reveals insights in leukemic transformation of bone marrow failure syndromes

Acquired aplastic anemia and severe congenital neutropenia (SCN) are bone marrow (BM) failure syndromes of different origin, however, they share a common risk for secondary leukemic transformation. Here, we present a patient with severe aplastic anemia (SAA) evolving to secondary chronic neutrophilic leukemia (CNL; SAA-CNL). We show that SAA-CNL shares multiple somatic driver mutations in CSF3R, RUNX1, and EZH2/SUZ12 with cases of SCN that transformed to myelodysplastic syndrome or acute myeloid leukemia (AML). This molecular connection between SAA-CNL and SCN progressing to AML (SCN-AML) prompted us to perform a comparative transcriptome analysis on nonleukemic CD34high hematopoietic stem and progenitor cells, which showed transcriptional profiles that resemble indicative of interferon-driven proinflammatory responses. These findings provide further insights in the mechanisms underlying leukemic transformation in BM failure syndromes.

Precision medicine in myeloid malignancies

Myeloid malignancies have always been at the forefront of an improved understanding of the molecular pathogenesis of cancer. In accordance, over the last years, basic research focusing on the aberrations underlying malignant transformation of myeloid cells has provided the basis for precision medicine approaches and subsequently has led to the development of powerful therapeutic strategies. In this review article, we will recapitulate what has happened since in the 1980s the use of all-trans retinoic acid (ATRA), as a first targeted cancer therapy, has changed one of the deadliest leukemia subtypes, acute promyelocytic leukemia (APL), into one that can be cured without classical chemotherapy today. Similarly, imatinib, the first molecularly designed cancer therapy, has revolutionized the management of chronic myeloid leukemia (CML). Thus, targeted treatment approaches have become the paradigm for myeloid malignancy, but many questions still remain unanswered, especially how identical mutations can be associated with different phenotypes. This might be linked to the impact of the cell of origin, gene-gene interactions, or the tumor microenvironment including the immune system. Continuous research in the field of myeloid neoplasia has started to unravel the molecular pathways that are not only crucial for initial treatment response, but also resistance of leukemia cells under therapy. Ongoing studies focusing on leukemia cell vulnerabilities do already point to novel (targetable) "Achilles heels" that can further improve myeloid cancer therapy.

Activation of 4-1BB signaling in bone marrow stromal cells triggers bone loss via the p-38 MAPK-DKK1 axis in aged mice

Senile osteoporosis can cause bone fragility and increased fracture risks and has been one of the most prevalent and severe diseases affecting the elderly population. Bone formation depends on the proper osteogenic differentiation of bone marrow stromal cells (BMSCs) in the bone marrow microenvironment, which is generated by the functional relationship among different cell types in the bone marrow. With aging, bone marrow provides signals that repress osteogenesis. Finding the signals that oppose BMSC osteogenic differentiation from the bone marrow microenvironment and identifying the abnormal changes in BMSCs with aging are key to elucidating the mechanisms of senile osteoporosis. In a pilot experiment, we found that 4-1BBL and 4-1BB were more abundant in bone marrow from aged (18-month-old) mice than young (6-month-old) mice. Meanwhile, significant bone loss was observed in aged mice compared with young mice. However, very little data have been generated regarding whether high-level 4-1BB/4-1BBL in bone marrow was associated with bone loss in aged mice. In the current study, we found upregulation of 4-1BB in the BMSCs of aged mice, which resulted in the attenuation of the osteogenic differentiation potential of BMSCs from aged mice via the p38 MAPK-Dkk1 pathway. More importantly, bone loss of aged mice could be rescued through the blockade of 4-1BB signaling in vivo. Our study will benefit not only our understanding of the pathogenesis of age-related trabecular bone loss but also the search for new targets to treat senile osteoporosis.

The elevated level of IL-1α in the bone marrow of aged mice leads to MSC senescence partly by down-regulating Bmi-1

Osteoporosis is becoming increasingly prevalent with individual aging. Recent studies found that bone marrow mesenchymal stem cells (MSCs) undergo senescence along with the progression of age-related osteoporosis, leading to a decreased rate of new bone formation and fracture repair. The underlying mechanism of MSC senescence in the aged bone marrow has not been clarified yet. Here we found that MSCs from aged mice (12-month-old, O-MSCs) exhibited apparent senescent phenotypes compared with those from young controls (2-month-old, Y-MSCs), including lower proliferation rate, impaired self-renewal capacity, increased p16Ink4a expression and shifted differentiation balance to favor adipocytes over osteoblasts. Bmi-1, one of the main factors that regulate stem cell self-renewal, is dramatically decreased in O-MSCs. Knocking-down of Bmi-1 in Y-MSCs lead to cellular senescence, while over-expression of it rejuvenated O-MSCs. We further showed that the level of IL-1α is much higher in the bone marrow fluid of aged mice, which significantly inhibited Bmi-1 expression in MSCs. Our present study indicated that IL-1α, a key component of the senescence-associated secretory phenotype (SASP), is elevated in the aged bone marrow microenvironment, leading to decreased Bmi-1 expression in MSCs and consequently, MSC senescence.

ERVs-TLR3-IRF axis is linked to myelodysplastic syndrome pathogenesis

Toll-like receptors are mutated or overexpressed in up to 50% of patients with myelodysplastic syndrome (MDS). Endogenous retroviruses (ERV) trigger TLR3 leading to interferon regulatory genes (IRFs) activation. We evaluated if the ERVs-TLR3-IRF axis activation would be linked to MDS pathogenesis and we also conducted a detailed cancer analysis of the ERVs, TLR3 and IRFs gene expression in 30 cancer types using GEPIA database. Seventy-nine bone marrow samples from patients with MDS were evaluated for cytogenetics and quantitative real‑time PCR of TLR3, ERVK6, ERVW-1, ERV3-1, IRF3 and IRF7. Patients with dyserythropoiesis showed higher TLR3 (p = 0.035), ERVK6 (p = 0.001), ERVW1 (p = 0.045) and ERV3-1 (p = 0.016) expression than patients without dyserythropoiesis. Upregulation of Interferon Regulatory Factors, IRF3 and IRF7, was associated with poor prognostic markers in MDS such as > 10% of blasts (p = 0.003-IRF3; p = 0.009-IRF7), low platelets count (< 50.000/mm³) (p = 0.001-IRF3; p = 0.021-IRF7), transfusion dependence (p = 0.014-IRF3) and chromosomal abnormalities (p = 0.036-IRF7). We found strong correlations between ERVK6-ERVW1 (r = 0.800; r² = 0.640; p = 0.000), ERVW1-ERV3-1 (r = 0.715; r² = 0.511; p = 0.000), and IRF7-IRF3 (r = 0.567; r² = 0.321; p = 0.000) and moderate correlation between ERVK6-ERV3-1(r = 0.485; r² = 0.235; p = 0.000), ERVW1-IRF7 (r = 0.389; r² = 0.151; p = 0.001), ERVW1-IRF3 (r = 0.357; r² = 0.127; p = 0.004), ERV3-1-IRF7 (r = 0.314; r² = 0.098; p = 0.009), and ERV3-1-IRF3 (r = 0.324; r² = 0.104; p = 0.007). Using GEPIA Database in 30 cancer types, we detected a typical pattern of upregulation as here presented in MDS. We suggest TLR3 activation by ERVs is linked to MDS pathogenesis leading to bone marrow failure. Abnormal double-stranded RNA (dsRNA) expression of Endogenous Retroviruses (ERV) triggers TLR3 hyperactivation. This induces IRF3, IRF7, and NF-kB to translocate to the nucleus and activate transcription of IFNα/β which binds to the type I-IFN receptor promoting interferon response. Thus, just as TLR4 induces a crucial myeloid shift, the ERVs-TLR3 axis may play an important role in establishing one of the most striking characteristics in MDS, dyserythropoiesis.

Mesenchymal Stromal Cells as a Cellular Target in Myeloid Malignancy: Chances and Challenges in the Genome Editing of Stromal Alterations

The contribution of bone marrow stromal cells to the pathogenesis and therapy response of myeloid malignancies has gained significant attention over the last decade. Evidence suggests that the bone marrow stroma should not be neglected in the design of novel, targeted-therapies. In terms of gene-editing, the focus of gene therapies has mainly been on correcting mutations in hematopoietic cells. Here, we outline why alterations in the stroma should also be taken into consideration in the design of novel therapeutic strategies but also outline the challenges in specifically targeting mesenchymal stromal cells in myeloid malignancies caused by somatic and germline mutations.

Putative Mechanisms Underlying Cardiovascular Disease Associated with Clonal Hematopoiesis of Indeterminate Potential

Characterized by the expansion of somatic mutations in the hematopoietic lineages of aging individuals, clonal hematopoiesis of indeterminate potential (CHIP) is a common condition that increases the risk of developing hematological malignancies and cardiovascular disease (CVD). The presence of CHIP-associated mutations in hematopoietic stem and progenitor cells (HSPCs) suggests that these mutations may alter the functions of the diverse hematopoietic lineages, many of which influence the pathogenesis of CVD. Inflammation may be a potential pathogenic mechanism, linking both CVD and hematological malignancy. However, it remains unknown whether CHIP-associated CVD and hematological malignancy are features of a common disease spectrum. The contributions of CHIP-associated mutations to both CVD and hematological malignancy underscore the importance of stem cell biology in pathogenesis and treatment. This review discusses possible mechanisms underlying the contributions of multiple hematopoietic lineages to CHIP-associated CVD and the putative pathogenic links between CHIP-associated CVD and hematological malignancy.

Hypoxia-mediated changes in bone marrow microenvironment in breast cancer dormancy

Breast cancer (BC) remains a clinical challenge despite improved treatments and public awareness to ensure early diagnosis. A major issue is the ability of BC cells (BCCs) to survive as dormant cancer cells in the bone marrow (BM), resulting in the cancer surviving for decades with the potential to resurge as metastatic cancer. The experimental evidence indicates similarity between dormant BCCs and other stem cells, resulting in the preponderance of data to show dormant BCCs being cancer stem cells (CSCs). The BM niche and their secretome support BCC dormancy. Lacking in the literature is a comprehensive research to describe how the hypoxic environment within the BM may influence the behavior of BCCs. This information is relevant to understand the prognosis of BC in young and aged individuals whose oxygen levels differ in BM. This review discusses the changing information on vascularity in different regions of the BM and the impact on endogenous hematopoietic stem cells (HSCs). This review highlights the necessary information to provide insights on vascularity of different BM regions on the behavior of BCCs, in particular a dormant phase. For instance, how the transcription factor HIF1-α (hypoxia-inducible factor 1 alpha), functioning as first responder under hypoxic conditions, affects the expression of specific gene networks involved in energy metabolism, cell survival, tumor invasion and angiogenesis. This enables cell fate transition and facilitates tumor heterogeneity, which in turn favors tumor progression and resistance to anticancer treatments Thus, HIF1-α could be a potential target for cancer treatment. This review describes epigenetic mechanisms involved in hypoxic responses during cancer dormancy in the bone marrow. The varied hypoxic environment in the BM is relevant to understand the complex process of the aging bone marrow for insights on breast cancer outcome between the young and aged.